feat: initialize monorepo structure with Bun and Turborepo

- Add package.json for the root with workspace configuration and scripts
- Create @gruperly/config package with TypeScript configuration
- Establish shared package @gruperly/shared with Zod schemas for validation
- Implement group, student, and payment schemas using Zod
- Set up TypeScript configuration for shared package
- Document stack architecture and technical specifications in stack.md
- Configure Turborepo with build, dev, lint, and typecheck tasks

packages/config/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "@gruperly/config",
+  "version": "0.1.0",
+  "private": true,
+  "type": "module"
+}